The Mess at Fukushima, and The Need for a Scientific Lens

Ever since the horrific earthquake, tsunami and ensuing nuclear accidents hit north-eastern Japan in March of 2011, the world has been keeping an eye on Fukushima, where the Fukushima Daiichi nuclear power plant suffered extraordinary amounts of damage. Initially the news out of the power plant, operated by the company TEPCO, was awful, but gradually the situation seemed to be increasingly under some control. But that control has not been convincingly secured, and has even perhaps been slipping of late. And the worries about a variety of possible risks from the plant have been growing, especially because the clean-up at the plant is still run by TEPCO, which has engaged in repeated cover-ups and poor decisions… not to mention the fact that it’s a power company, not a nuclear accident site cleanup company. I find it extraordinary that the situation hasn’t been put into the hands of a blue-ribbon international panel of nuclear scientists and engineers, with full power to make decisions and with full transparency for all to see as to what is going on. It’s taken the Japanese government far too long to step in.

I’m bringing this topic up now because TEPCO is finally ready to address one of the major issues that they face in the clean-up. In addition to finding ways to deal with the melted-down nuclear fuel at Reactors 1, 2 and 3, which will take years, they have to deal with the stored and mostly undamaged fuel rods that are sitting outside of Reactor 4, in a water-filled pool. The water keeps the fuel cool, and right now there’s nothing wrong with the pool or the cooling. The problem is that this pool is on the 3rd floor of the Reactor 4 building, which was damaged in a (chemical, not nuclear) hydrogen explosion shortly after the earthquake… and it would be better to get the fuel rods into a safer pool, at ground level, outside of the compromised building. This is not easy for many reasons, and apparently there is some risk involved — not risk of a nuclear explosion, which is physically impossible in these circumstances, but of some amount of radioactive gas being produced and released into the atmosphere if the fuel rods are not kept submerged in water or are otherwise damaged. However, I’m not precisely clear on the nature of this risk.

There are good reasons to be concerned that things are at risk of getting out of hand on many different fronts, both in terms of actions on the ground and in terms of public understanding. On the one hand, I’m reading more and more scare-mongering: irresponsible statements made by non-experts, such as the ones about starfish, that are starting to frighten my friends and neighbors unnecessarily, especially on the west coast of the United States. (Here’s a response by a deep-sea biologist to one of the most egregious; I can’t directly verify all of the points he makes, but many of them were obvious to me even before I found his website.) On the other hand, I’m not at all convinced, given their terrible track record, that TEPCO is capable of dealing with the extreme technical difficulty and considerable danger of putting their nuclear plant back into a safe condition without there being additional significant releases of radioactive material. And meanwhile, media reporting is just not sufficiently reliable; the journalists aren’t experts and often don’t understand the issues well enough to get it all straight or put it in proper context.

If there were ever a time when level-headed scientific discussion, careful calculation and thoughtful consideration were needed in a public setting, this would be it.

I haven’t yet found a sensible, trust-inspiring blog that does for nuclear engineering and radiation safety what I try to do for particle physics (though this one looks somewhat promising.) Consequently, I don’t really have a way to understand the whole story and to gauge it properly. So I’d like to find a way to use my website and its readers, some of whom surely know more about nuclear engineering and radioactivity risks than I do, and some of whom are perhaps getting more information than I am, to assemble a clearer understanding of what the risks and dangers really are and are not.

Fair warning: In contrast to my usual policy, I am going to be strictly editing the comments on this post, and all similar posts on Fukushima. I will accept thoughtful scientifically-based discussion, and links to such discussion, only. I want neither my own mind nor my readers’ cluttered with unscientific chatter from non-experts. Polemical diatribes will be deleted; activism for or against nuclear power is inappropriate here [I happen to oppose nuclear power in its current form, but that’s beside the point right now]; and unscientific assertions without any support from replicated studies will be marked as such, and if sufficiently egregious, deleted. My goal is the same as that of most people: to get a better grasp of the situation, and to get a clearer sense of what to worry about and what not to worry about, both for now and looking into the future.

So: do I have any readers with expertise in this area? If you’re one of them, can you help us establish a baseline of solid science that we can build on? Does anyone know of particularly even-handed and sensible blogs by experts that we can draw on? Websites with data or resources that are run by people without an obvious big axe to grind? One of the big problems I find is that there are plenty of scientific studies quoted on blogs, but few guides to the non-expert reader to help us put the results in precise perspective.

By the way, here’s one site that shows the radioactivity levels in and around Berkeley, California; as far as I can see, nothing above normal levels has been measured for well over a year, and never were levels high even in 2011. http://www.nuc.berkeley.edu/UCBAirSampling

79 responses to “The Mess at Fukushima, and The Need for a Scientific Lens”

[Editor’s caution: I would like to note up front that I feel this comment isn’t sufficiently clear and precise about this topic, and as written would potentially confuse and unnecessarily scare a non-expert. See my comment on it below.]

To start with, thanks a lot Matt for bringing this subject to the discussion.

IMHO, this is a matter that requires the proper professionals to conduct such an argument, that is, nuclear engineers and physicists involved in the R&D process of research nuclear reactors.

For full disclosure, I’m both and industrial engineer and chemical engineer by training, so, I exclude myself as being somebody that could properly provide deep and thorough feedback on the main issues pertaining to this disaster and its cleanup.

Having said that, I would also like to add that on many of the classes that I studied on industrial and chemical processes, the faculty members were all nuclear engineers and PhDs (on physics and chemistry) from the National Commission for Nuclear Energy (Argentina’s state run agency in charge of all uses of nuclear energy), so, all examples that we were given as students were completely focused on the industrial production of energy in nuclear reactors, from the problems regarding the manufacturing of fuel rods, to all the processing problems regarding the conversion of yellowcake to fuel pellets, to the multiple engineering problems that have to be solved for a succesful design of a water-cooled nuclear reactor.

As such, I do have some more background and understanding of the main issues at hand in this accident that what could expected from either a lay-person or even the average engineer.

Up to a point, this accident has many points of contact with the accident at Three Mile Island, or even the Chernobyl accident.

All these reactors had an old design with a very clear vulnerability in the lack of a fail-safe mechanism that could cool off the decay heat (the excess heat that still affects the fuel rods after the reactor is automatically turned off in the face of an adverse event like the earthquake or the tsunami).

The cooling off of the decay heat is critical, because, if it is not carried out properly, the fuel rods will be negatively affected, even up to the point of melt-down: this is something that should never happen, because it is way too dangerous.

All these “old design” reactors depend on electrical pumps to cool off, so, this critical process depends on the perfect function of an instrumentation and control mechanism to cary out a very critical operation. This is an awful design, what was the design of the first generations of reactors.

Newer generations of nuclear reactors have decay heat cooling off mechanisms that are much, much more reliable to work and deliver what is so critical: a cooling off of the fuel rods according to the proper curve to keep these rods within operational conditions at all times.

Well, cutting to the chase, in the aforementioned accidents, including Fukushima, this mechanism failed so badly that many fuel rods got melt down.

As the fuel rods are cooled by water, during this major failure, this water got into contact with the materials of the fuel rods, including its contents (bear in mind way before melt down, the fuel rods broke and allowed water to get in contact with its contents).

So, now we have water and some stuff that it is not expected to be in contact, and all of these (the water, the contents of the rods and the rods themselves) are at high temperature with the temperature rising.

Very soon, some really unwanted chemical reactions start, with one of them being a very undesidered and dangerous: the generation of hydrogen gas.

The build-up of hydrogen gas with a nuclear reactor is lethally dangerous, because, it is both a gas and (in the presence of oxygen), it is extremely explosive.

Nuclear reactors are contained within a specially designed case with the main purpose to contain within it any internal leakage of radioactive material, but this case, even though it is rather strong, cannot withstand a powerful internal explosion and remain unscathed.

In the three accidents, the coof off mechanism failed. The differences between the three accidents are related to how far into the melt-down of fuel rods, the generation of hydrogen gas, the build-up of it within the case, and the misshandling of this build-up this process went.

Once the containment case of the reactor is compromised, one way or another, you have a nightmare come true with radioactive material leaking into the environment, with the help of one or more fluids transporting this dangerously contaminated material into the surrounding habitats: water and/or gases with both high temperature and high pressure.

So, thank you GEN, but I’m afraid I’m going to criticize this comment — constructively, I hope. Please don’t take it personally; you’re a wonderful contributor to this blog’s comment stream and I highly appreciate your presence here. But this is way too much like a journalism article, and not nearly enough like the type of explanation that I want to see on this website.

The problem with your comment is not that it is inaccurate, but that, for a non-expert reader, it’s nowhere near sufficiently clear, and frankly, as written, it is scary without being properly balanced.

For one thing, your discussion about the “melt-down of fuel rods” specifically refers to what happened in Reactors 1, 2 and 3. But you didn’t say so. So this leads to confusion. What’s happening at Reactor 4, involving the fuel rods in a pool of water being moved to another location, is not related to the melt-downs in Reactors 1 2 and 3. We have to be precise here about what we’re talking about.

For another thing, you’ve said “nightmare” and “radioactive material leaking into the environment”, but this isn’t quantitative or scientific — it’s just scary-sounding. You’re not separating and distinguishing what happened in March 2011 (when there was a lot of radioactive material released) from what happened later in 2011 (when the amount was greatly reduced but still significant) from what happened in 2012-2013 (when the amounts were quite small, even by comparison with late 2011.) How is a non-expert reader to know the difference between past leaks, present leaks, and potential future leaks, and to compare their size and risks?

I could go on with this. So I’m going to note on your comment that I don’t endorse it and that readers should be cautious because it is insufficiently clear and precise. I want a higher level of comment here: precise statements, quantitative comparisions, explanations that either are or can be made clear to a non-expert — it’s a high bar I’m seeking. And that means that no one comment can give the whole story, because you can’t tell the whole story without being imprecise.

Matt, all you have said is correct, even more so because you gave proper warning ahead of hand, which I really appreciate.

Being myself an engineer, I can only encourage and validate the approach you want to pursue with this particular discussion.

Engineers and scientists in general share the need of the use of proper definitions and of quantitave and precise descriptions of a problem at hand.

It is a laudable effort of yours to follow that path for this forum, and, as I said, it should involve nuclear engineers and scientists involved in the design and development of both research and commercial nuclear reactors.

So, in order to be educated readers, one of the tasks that we have ahead of us is to establish the nature of the hosts of websites like this one; do they have a natural or strong bias? why does this website exist? is it an individual with training, or an organization with a particular raison-d’etre? how much training do these people have and in what field? etc.

So: we go to the website and we click “About Us”. And we learn that the director is

Maggie Gundersen founded Fairewinds Energy Education, a 501(c)3 non-profit organization, in 2008. Its mission has remained to educate the public about nuclear power production, engineering, reliability, and safety issues. Maggie also founded Fairewinds Associates, Inc, a paralegal and expert witness services firm in 2003. She has a history as well expertise within the nuclear power industry. Maggie began her career with a position in Combustion Engineering’s reload core design group, after which she was the public information specialist at a proposed nuclear power plant site in upstate New York. During her last position with the nuclear power industry Maggie, an executive recruiter, placed the vice president of operations with the American Nuclear Insurers.

Not obviously an expert herself, right? The “public information specialist” is not necessarily herself knowledgeable about the science. But there’s a chief engineer:

“Arnie Gundersen has more than 40-years of nuclear power engineering experience. He attended Rensselaer Polytechnic Institute (RPI) where he earned his Bachelor Degree cum laude while also becoming the recipient of a prestigious Atomic Energy Commission Fellowship for his Master Degree in nuclear engineering. Arnie holds a nuclear safety patent, was a licensed reactor operator, and is a former nuclear industry senior vice president. During his nuclear power industry career, Arnie also managed and coordinated projects at 70-nuclear power plants in the US.”

An engineering expert, but deep within the nuclear power industry. Potentially a very big conflict of interest. Then we have

“Dr. Leslie Kanat has been a professor of geology at Johnson State College for 23 years. In addition to being on the Fairewinds board, Les is also on the board of the Vermont Geological Society, and is a member of the Vermont State Nuclear Advisory Panel.”

and

“Lucas [Hixon] is from Chicago, where he writes and conducts much of his research. He is the founder of Enformable, and is a preeminent nuclear researcher.”

All in all I can’t do much with this. Can anyone give me more information about these people and what their goals are? They say: “Our mission is to educate the public about nuclear power and other energy issues. We have designed our website to be a hub for fact-based, unbiased nuclear energy information.” But everyone says that. How can we establish that in fact their goals are what they say they are? This is the essential problem in information gathering…

Stanley, can you help us here? Do you know something about these people, or are there things on the website that have helped you become confident in their reporting?

We should be very careful with sources (websites) that may be sponsored by special interest groups, industrial lobbies or even specific companies with high stakes in the business of utilities in general, or nuclear power plants in particular.

It would help to see if the websites include a full disclosure statement.

Ok, here’s a quote from Arnie Gunderson that we can try to track down: in a presentation that he gave “At a full-house public lecture in Kyoto on Sept. 3rd, 2012, organized by Green Action in conjunction with several other local NGOs, Arnie lived up to his reputation for forthright condemnation of the nuclear status quo” (so now we learn who he is: he has a strong anti-nuclear activist bias, which doesn’t mean he’s wrong but means we have to verify what he says carefully).

Here’s the quote:

““The reason that the American NRC ordered an evacuation [after the Fukushima disaster began] was because of the possibility of a fuel pool fire at Unit 4. In 1997, the American Brookhaven National Laboratory did a study that showed that if a nuclear fuel pool were to boil dry, it would release enough radiation to cause the permanent evacuation of an 80-kilometer circle… They also know from this study that there would have been hundreds of thousands of cancers caused by a fuel pool fire, depending on population density.

“Nuclear fuel rods are made of a material called zircaloy, which burns in air with a fire that burns in air with flame that water cannot put out. Two weeks before the accident at Fukushima Daiichi, Sandia National Laboratory ran a test to see if a nuclear fuel bundle could really burn in air. Nuclear heat was simulated with electric heaters, and the nuclear fuel began to burn.

“The Daiichi Unit 4 pool does not have one bundle [of fuel rods], it has 1,500 bundles. There is more cesium in that pool than was ever released into the Earth’s atmosphere from all of the 700 nuclear bombs exploded in over 30 years of nuclear weapons testing. There is the concern that scientists around the world have today, that the Daiichi Unit 4 pool is still in jeopardy of boiling dry, and of course if that occurs, a massive evacuation would be necessary.”

1. Can someone help me find the Brookhaven National Laboratory report? And what does it mean “release enough radiation to cause the permanent evacuation…” How quickly? Over what time period? With what assumptions? Gunderson is giving a lecture, so he’s speaking quickly: this is not scientific information, it’s just a partial description of scientific information, and that’s not sufficient for our purposes.

2. Can someone help me find more about this Sandia National Laboratory test and its results?

3. What precisely does Gunderson’s statement mean that “there is more cesium in that pool…” how much of this cesium could potentially get into the atmosphere, and again, how fast, and where would it most likely go? Are there any mitigation procedures that could be used to deal with this risk? And what exactly are the risks, not if the pool as a whole boils dry, but if control is lost for one of the fuel rod bundles? Let’s start one at a time and work our way up.

If for any reason there was a rapid loss of water from the Unit 4 storage pool exposing all of the used fuel to air, the used fuel can’t catch fire or melt because it has been cooled for more than two and-a-half years and no longer generates enough heat to damage itself. The used fuel in the pools at the other three damaged Fukushima units is even older and colder.

Now this is something that we should be able to turn into science: a calculation, not words. Either this statement is true or it is not: either the fuel, after two years becoming less radioactive as it sits in the pool of water, can heat itself to the ignition temperature of the zirconium alloy that is the fire risk, or it cannot. So — who can help us find this calculation in the scientific literature? Or can help us work it out on our own, and then check it with an expert?

Ok, I spent some time skimming the following US Nuclear Regulatory Commission report from 2000: http://pbadupws.nrc.gov/docs/ML0037/ML003727905.pdf. I suspect this is the same one that gave the nuclear-industry guy the confidence to claim that there’s no risk from 2.5-year-old spent fuel rods — that even in the absence of water they can’t heat up enough to cause a zircaloy fire.

Anyone who might think that way based on this report clearly didn’t read the report carefully. It seems to be a very well-written, solid paper, and the authors did a laudable job of listing all of the assumptions that are made when doing their calculations. And I quote from page 23 (which, if you read it, you will see is not out of context): “It is important to keep in mind the limitations (noted earlier) of these predictions at elevated temperatures. The 2 and 3 year results reach temperatures where the lack of radiation and chemistry models is expected to affect the solution.” In short: they are not keeping track of a few nuclear and chemical reactions that would occur at the highest temperatures, and these make their results uncertain… and probably underestimates, since those reactions would generate additional heat.

Moreover, they assumed there was no damage to the fuel rods, and that the rods are uniformly distributed across the pool where they are supposed to be. I believe that any such damage or closer spacing than intended could cause local additional heating.

Finally, there’s something else that Arnie Gunderson said that I hadn’t appreciated. There are about 1500? 1300 “assemblies” or “racks” or “bundles” (do I have the terminology right?) of spent (that is, used) fuel rods in the pool. The spent fuel is highly radioactive after it is used (which means many nuclei in the fuel are decaying away, generating heat among other things) but it gradually becomes less radioactive over time. However, there are also 200 assemblies of unspent (that is, unused and ready-to-use) fuel. These aren’t very radioactive and won’t generate any heat at all — unless they get too close together, in which case the very chain reaction that powers a nuclear reactor could start. To quote Gunderson: “I build fuel racks, and I know that the gap between the fuel is really, really critical. If the fuel gets too close together you will get a chain reaction. That’s not something you want to happen in the fuel pool.” You don’t want it to happen in a fuel pool because the heat generated will boil away the water in the pool and heat up the other fuel, not to mention generating radioactive material that won’t be safely contained inside a reactor containment vessel. So it appears that Gunderson is worried that a TEPCO screw-up could lead to having unused fuel too close together and the start of a nuclear reaction that in the end could lead to a zircaloy fire involving the spent fuel — or something like that. Perhaps this is part of why TEPCO is moving the unused fuel first? It is also probably safer to move less radioactive fuel…

Anyway, I’m not particularly inclined to believe the NEI nuclear expert’s reassurances, based on reading this report.

Excellent find, though still rather confusing. We may need an expert to help us assess it.

Do you understand slides 9 and 10? There aren’t enough words to go with the equations and figures…

Slide 12 contains simple but very important comments; in particular there is no fixed “ignition temperature”, the issue is also the environmental conditions in which the heating is occurring.

A very important issue is that zirconium alloy slabs don’t burn easily; powders do. The implication of this and other remarks is that damaged zirconium alloy may be more prone to ignite than flat slabs, so a key issue is to check that the zirconium cladding hasn’t been damaged in the explosion that ruined the Reactor 4 building, and to assure no further damage occurs while moving the fuel rods around.

Allow me to give some feedback on this entire affair of the risks pertaining to spent fuel rods at Fukushima.

The outer layer of the fuel rods is called cladding, its main purpose is to provide a corrosion-resistant cover to avoid radioactive material from within the rods to enter in contact with to coolant.

The cladding in the fuel rods used by Fukushima is Zircaloy. This is a concern because the Zirconium in Zircaloy can ignate in the presence of oxigen, but the conditions for that ignition to start depend on many parameters.

Of those many parameters, the thickness of the Zirconium layer in the cladding is the main one: the thinner the layer of Zirconium in the cladding, the lower the temperature that could ignite the fuel rod in contact with oxygen.

The first equation in slide 9 is the famous Arrhenius equation: very simple but remarkably accurate.

It indicates the relationship (dependency) between the rate of a chemical reaction and temperature, with all other variables of the reaction being constant.

The second equation is the classic heat loss of heat dissipation equation.

IMHO, tt would be useful to gather status report information on the Fukushima plant regarding all open issues and concerns, like say, what the International Atomic Energy Agency shares with the public regarding this said status:

It would also be useful to see if there are other technical reports from the international community of science and engineering, so as to have a broader, informed image of the problems.

There are many sides to this problem, and we do not have enough information at first to distinguish the factual, imparcial accounts of the current issues from the biased accounts from sources that may have stakes rolling on the dice with the clean-up process.

It is interesting to think about how many people have been so far killed in nuclear accidents (about 100, some sources tell more) and how many people have been killed in hydro-electric accidents (about 200,000).

Your second comment is borderline-in-conflict with my rules for comments on this page; we are trying to understand the risks of Fukushima, not debating the relative merits of nuclear power versus other forms of power. Worse, your comparison is highly unscientific. Hydro-electric accidents are mainly due to failed dams, the worst of which occurred in third-world countries with poor dam-building procedures, not in highly developed countries like Japan, the US and Europe. 90% of these deaths occurred in one 1976 incident in China, http://en.wikipedia.org/wiki/Banqiao_Dam. The number of deaths attributed to dam failure is in highly-developed countries since 1945 (the only fair comparison, since there was no nuclear power before then) is in the low thousands — maybe 4000. I don’t even know which of those dams were built for power, as opposed to water supply, and neither do you, I’m sure. So please — don’t just throw numbers around like that. This is precisely what I am trying to avoid.

Regarding this issue and the importance of being “laser-beam” precise with each description and definition and avoid non-scientific comments, it brings to mind how crucial and pivotal was the participation and feedback of Richard Feynman in the investigation of the accident of the Challenger, which, by mere coincidence, was vividly portrayed this past weekend in a really good movie in a joint telecast on both Discovery Channel and The Science Channel.

To me, Feynman’s final comments in his appendix to the report are a clear guidance and beacon to the kind of analysis that Prof. Strassler wants to pursue:

“For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.”

For further details, with no further ado, all interested parties so go to the source:

Matt,
Kudos for addressing this issue – certainly much of the discussion regarding nuclear power in general and Fukushima in particular is scientifically uninformed, to put it mildly. I support all attempts to facilitate a more educated discussion.
Having said that, if your goal is to “establish a baseline of solid science that we can build on”, and the “we” is the average person reading this blog, I think nuclear engineering is several rungs too high up the ladder for starting the discussion. In my experience the average person does not even know what the word “radiation” means, or, that, in fact it has several different meanings. While I am sure that your readers are better informed about science than the typical person, I do not think you can assume that the majority of them even know the difference between, for example, alpha particles and microwaves.
If you really want to provide a baseline for discussion, I therefore suggest you proceed on two parallel tracks. The first you have already started, for those that have a rudimentary understanding of nuclear science, but are not experts, and want to be more informed about exactly what is going on at Fukushima. The second track would start from the ground floor, and begin with something like “What is radiation?”. Of course I realize that I am suggesting to you twice as much work (or maybe more!). I am not a nuclear engineer, so I cannot help with the first track. However I am a physics professor and have a great deal of experience teaching non-scientists about radiation. Your explanatory skills are outstanding, but if you wanted assistance with the second track for time’s sake, I would be willing to volunteer.

That is indeed my plan, Kent. But I’m not quite educated enough to run the second track yet at the level of clarity and relevance that I would aspire to. My goal is to get to that point. And I would like your comments/corrections with anything I put up about radioactivity for the non-expert.

Great. I certainly will comment when the time comes. Before you start, I will share with you the following points I have found to be essential to overcome common misunderstandings with radiation.
1. Distinguish among the various definitions of radiation. Point out that in the context of nuclear power it is ionizing radiation which is important. Even after explaining the difference, I still have have to check an audience member’s cell phone with a Geiger counter to prove “cell phone radiation” is not radioactive.
2. Explain that even ionizing radiation is made out of the same particles that make up ordinary matter. The names “alpha, beta and gamma” sound “spooky”, but helium nucleus, electron, and light particle do not.
3. Following from point 2, ionizing radiation is not inherently toxic or contagious. It is dangerous because of the large amount of kinetic energy contained in the particles (analogy: a baseball is not inherently dangerous, but you wouldn’t want one hitting you at 90 mph!)
4. Radiation is naturally occurring from rocks, cosmic rays, etc. Not only is it impossible to avoid all exposure to ionizing radiation, it is not desirable to do so (a small percentage of all potassium, an essential nutrient, is radioactive,)

Once people understand these key points, they are ready to learn about the potential harms and benefits of various types and dosages of radiation exposure.

Thank you Kent; these were on my list, but you’ve added some details I should definitely include. If you have any further suggestions, especially subtle ones that might easily be overlooked, please do forward them.

The concern regarding the spent fuel rods is whether or not the current operational conditions of those rods at Unit 4 could lead to a spontanous fire in the future, before they are removed for processing.

This depends on many factors, many such factors that require to be measured in situ to have a better calculation of the likelyhood (probability) of a spontaneous fire.

The current temperature of the rods, which a result of both the decay heat and the dissipation of heat by the coolant, but the actual dissipation is affected by the level of coolant in the pool.

It could be calculated (and it should be calculated) what is the threshold height of spent fuel rod not covered by coolant that could create an increase (instead of a decrease) of temperature in the spent fuel rods.

It is clearly known that air is not good enough a coolant to dissipate decay heat, so, fuel rods that are not sufficiently covered by coolant do have a threshold height (not covered by coolant) when the temperature will increase.

Since this scenario is something to control and avoid, it must be known in a quantitative and precise manner to be able to be controlled to be avoided.

if this rise of temperature gets to the point of ignition for Zr in contact with oxygen (that temperature depends on many factors, including the thickness of the outer Zr layer), that is the main issue with these rods at Unit 4.

I have not been able to gather enough info to assess what would be the likely ignition temperature for those rods at Fukushima, but the fact that there is a new reccomendation regarding using other materials for cladding, like ceramic Silicon Carbide, it seems to point in the direction that the likely ignition temperature is within the range that could happen by accident if not properly monitored.

Clearly, monitoring the conditions of the spent fuel rods at the staging pool may not be economically feasible, so, a different design of the cladding looks more reasonable.

It would search for and try to validate info on the likely ignition temp for these rods.

I am a little confused what you are actually asking about? I know a few nuclear engineers, as well as some medical personel who are specialized in radiation treatment. Are you asking specifically about the current safety risk to humans from Fukushima (a medical question), or more about what the dangers that are in a specific reactor or perhaps a specific procedure for winding the plant down?

A lot of the engineering details are terra incognita, so it shouldn’t be a surprise if experts disagree over specific technical details in this case and I very much doubt the internet is a good place to get any sort of reliable information. As a general rule, I have a great deal of confidence in the nuclear engineers in Japan, they really do have some of the worlds best people in this area and it is highly likely that they are at least informing the engineers at Tepco (whether their advice is heeded I have no idea about).

The answer is both, because the public needs to know both, and to know how they fit together into an overall picture of risk.

I also have a lot of confidence in the engineers in Japan. But I do not have a lot of confidence in TEPCO’s ability to *manage* the situation, partly because I’m not sure the managers actually listen to their best engineers.

To quote one of my colleagues: “Wikipedia is a great place to start your research; it is a terrible place to end it.” There’s nowhere near enough scientific documentation for the majority of the statements about risks.

I doubt that any credible calculation about the probability of an ignition of the rods in Fukushima Unit 4 can be done.
If the rods were in a known state, such as they come out new from the factory, or spent in a regular way, and then stored in an ordered scheme with a known geometry and spacing between these rods – this would be a situation that could be handled with approximate calculations of the temperature distribution in space and time, and a probability for ignition.
But the situation is different. Some of the rods are probably damaged, in a way that is not exactly known. The rods may have undergone temporary heating, while they were exposed to the air, before more water was introduced in the plant. Cooling was done to a large amount by sea water, which causes much more corrosion and atypical damage to the rods.
Also, the current geometry of the rods is not well known. Two earth quakes and the attempts to cool the rods in a hurry are likely to have disturbed the original geometry. The plant may have an inclination now, and material from above may have fallen onto the rods.
No one knows the exact condition these rods are in. Some of the 1500 or so rods may be in good condition, but it would be very highly optimistic to assume that all the rods are in a well-defined state that allows an engineer or a physicist to calculate hard numbers.
I think the only way to assess the situation and to make a guess about the probability of an ignition is to make in-situ measurements of temperatures, chemistry, take photos or videos of the situation. And if this is not possible, or only to a very limited extent, due to the high radiation level and blocked access, one should be honest and admit that no reliable estimate for this situation is possible.

Markus — I am tending to agree with this assessment. The uncertainties appear to be very great, and most of the unknowns seem to contribute to an increase in the maximum possible temperature. This is a serious problem and makes all blanket reassurances somewhat questionable.

However, there must be more to learn about the maximum possible temperature and the greatest possible risk of reaching that temperature, so we should try to determine the upper bound of the risk…

The “worst case” may not come as one big bang but in several steps, and we may foresee only the first one or two steps with some clarity. A bad evolution would be a release of radioactivity from a damaged rod to such an amount that further access to the plant 4, and possibly also to the other plants at that site, would be much more difficult, or in practical terms, impossible for human beings. This would not be immediately an impact on large scales, but would drastically increase the risk of further damage to the plants. Even if the access were hindered only temporarily, say for some months, this would drastically increase the risk of other things going wrong, and possibly making large-scale events possible that were practically impossible if the plants could be orderly and permenantly cooled and maintained (which is already now not the case).
So I suggest to include such a cascade of events in the ensemble of scenarios for estimating the upper bound of the risk. (However, I doubt that credible probabilities can be assigned to such event cascades.)

Fair enough. I agree that such a cascade seems plausible as a worst-case scenario.

But in our conversation, I am noticing that I’m being careless: we’re talking about risk in three (or more) different ways… and we have to fix that.

One issue is the risk of a very bad scenario occurring, which can’t be calculated — the more bad things you imagine layering upon each other, the harder it is to guess the probability. For instance, we certainly can’t guess the probability that TEPCO can move all 1500 assemblies without a serious incident/accident occurring.

A different issue is what will be the *effect* of a bad scenario: what is the risk, if such and such a bad thing happens, of a certain amount and type of release of radioactive material into the environment? This might be calculable, to some extent.

And a third issue: what is the risk to human health, the local environment and to the local economy of such a release? This too might be calculable.

Let me add one more observation regarding “risk” vs. “effect” of a “bad scenario”: The first is a “technical” question as outlined by Markus Harder, and I really could not add anything to this. The later is a “biological”/”medical” question. A person qualified in one field is seldom qualified in the other field.

There are many different fields in which expertise is needed (and I’m sure there are more distinctions one could/should make, e.g. metallurgy), and the trick will be finding *both*
a) people with the necessary “depth” in one field
b) and people who maybe lack the “depth”, but have enough depth in many fields (“width”) to “compile” the information from the different fields.

I would say that a scientific approach is looking at past accidents to see which energy sources have been relatively less dangerous.
Let me tell two stories, which cannot substitute a serious analysis, but are significant in this direction.

First, the worst nuclear accident in history is almost unknown: Chelyabinsk-40. This was a secret Soviet military installation, where serious nuclear accidents happened in 1948, 1957, 1968. What is astonishing is that for propaganda reasons almost no safety measures were taken. Radioactivity was discharged in a river used for agriculture and for drinking: instead of informing people, Soviets forbid local doctors to diagnose cancer. This criminal act allows to learn what happens when half a million of persons are severely irradiated. The number of deaths is uncertain and is considered to be in the 100-1000 range.

Second: in Italy we had 1917 causalities in a single hydro-electric accident (Vajont, 1963). I am not throwing numbers.

Alessandro, I do not know much about the Chelyabinsk analysis, but I have no reason to disagree with your numbers in this case. However, I do want to again emphasize that it is not the purpose of today’s post to engage in a comparison of relative risks of different types of power, which in any case are not merely questions of numbers of deaths but are more complex issues, involving injury as well as death, evacuation and rebuilding issues, loss of usable land and economic damage to export industries, etc. There is also the problem, in making the comparison, that accidents in nuclear contexts are rare but are long-lasting, widespread and difficult to clean up, compared to dam breaks which are more common but whose effects are often more quickly dealt with. So there are many problems of comparing apples and oranges here.

The issue of demonstrating to the public that radioactivity is somewhat less dangerous and frightening than most people think is something that must also be addressed, and I do intend to deal with it to the extent the scientific literature is conclusive on the matter. The last thing I want to do is make people unnecessarily afraid of a natural process that they take for granted when they have a CAT scan or fly in an airplane or live in a stone building. Only after this is done, however, can a serious discussion comparing different types of power sources be undertaken. So I think you are putting the cart before the horse right now.

I think a couple of key questions regarding the pool in reactor 4 are :
What is the current temperature of the pool, and how is it behaving over time ?
Is water being added to and removed from the pool ?

I believe that as long as they have electric power and no holes in the pool, there’s no problem circulating water in and out of the pool and maintaining a constant temperature. I haven’t read anything that clearly suggests otherwise. If you have reliable sources that disagree, let me know.

I applaud your effort to cut through the thicket of alarmism on one side and mollifications on the other, in order to get to the “truth”!

I’m afraid there isn’t much I can add except one feeble observation: The main problem is going to be finding qualified people who are not currently employed by the nuclear industry (and don’t depend on employ there). I’m sure there are (somewhat) critical people within the nuclear industry, but it will be difficult for them to participate in a public forum.

As I said, it isn’t much that I can add to this discussion, and I wish you all good luck!

Oh, I’m not so worried about that. I find that many people seem to think that everyone is in the employ of someone else and so everyone’s view is hopelessly biased. This nihilistic view is not supported by my experience. You do have to be patient and careful in analyzing the data and the interpreters of that data… but there are many places to look for information. First, not everyone who works in the nuclear industry is gung-ho pro-nuclear (Gunderson, for instance, who has been mentioned several times); second, some people who are nuclear engineers work in regulatory agencies or have jobs at universities that do not depend upon funding from the nuclear industry; third, some people in the nuclear industry are very much in favor of building modern, safer plants and getting rid of these dangerous old ones, and will tell you why the old ones are so dangerous; etc.

A good example I am reading right now. Everybody knows that the Union of Concerned Scientists are not exactly pro-nuclear but Edwin Lyman, one of his nuclear experts collaborators, seems to have said that a chain reaction in the fuel pool was not a risk he considered significant.

“The biggest risk with Unit 4 pool unloading is that a spent fuel cask might drop and damage the pool, causing a leak that could expose some fuel and cause overheating,”

Spent fuel pools have automated handling systems to manage fuel rods and fuel rod assemblies (and just about every operation is done by these automated systems, with some specific operations being manually controlled but handled by the same equipment).

These handling systems are used to avoid accidents while managing the rods and assemblies.

Water in the pools have three main purposes: cool off decay heat from the rods, down to the proper operational temperature for fuel re-processing, shield radiation from the operators, so that they do not need any protection gear while working at the pool as long as the rods are in water, and protect the cladding (outer casing of the rods) from degrading.

At the time I was baffled by hydrogen explosions just blowing containment buildings away. Clearly the containment structures were meant to contain (hopefully minor) radioactive leaks, not hydrogen. They seem to be a standard feature of many designs. Maybe new guidelines should be developed for their usage; letting them explode in an emergency does not help.

Nuclear reactors have many redundant measures to mitigate the effects of a leakage of radioactive material to the environment.

Besides the fact that it is designed like a modern submarine, with an inner hull that is separated from the outer hull, the inner hull or containment case works with negative pressure, that is, the air is at a lower pressure than the atmospheric pressure, so that if there is any crack in the containment case, the negative pressure will avoid (or at least mitigate) the chance of anything escaping to the outside of the chamber.

Generation of hydrogen is a possible outcome in water-cooled reactors, so, the design of such reactors is such that it includes many redundant measures to mitigate the formation and build-up of hydrogen.

The major issue to really avoid is the build-up of hydrogen beyond the safety limits, but reactors are designed to handle some generation of hydrogen, as it is not economically feasible to completely avoid the formation of hydrogen.

“avoid .. the build-up of hydrogen beyond the safety limits”. In a critical situation there will be plenty of hot metal, whose reaction with water will produce hydrogen. This critical situation should certainly be avoided, but can we do anything when it happens? Can we detect that it has happened? Can we then vent the hydrogen? Remove the oxygen? Just sit down and wait?

Precisely because this is a very old design, there are many similar power stations. It might be possible – and maybe not prohibitively expensive – to prevent a hydrogen explosion scenario from happening again. Of course the price would be to allow some radioactive leakage, probably politically totally unacceptable.

The page referenced directly indicates the PROFUSION of methodologies and units to measure “radiation”. This page also references specific conversion tools – plug in microsieverts/hr return nanoGrey/hr, and the relation of Activity units to Dosage units: http://www.radprocalculator.com.
It’s useful for many conversions, but it’s particularly handy to do the complicated calculation for you to figure out the relation between ACTIVITY (Bq or Ci) and DOSE RATE (Sv, rem, etc.). Go to the site to learn why you can’t simply convert Bq (activity) measurements into dose rates (in µSv/h, etc.), where its FAQ section (on http://www.radprocalculator.com) clears up much:

I’d found this account about the situation around Chernobyl informative:http://www.kiddofspeed.com/chapter1.html
maybe it could be useful as a comparison. And it does address, right away,
the issue of illustrating what these different units mean, I think.

I have some experience in the nuclear industry, having worked as radioprotection technician for about 10 years. Although I am not directly involved, my company is directly supporting Tepco as engineering and technical consultant at Fukushima.
I find it important when discussing Fukushima incidents with non-experts to establish a reference point, and the regulatory release limits for nuclear power plants are a good start. These plants are authorized to release liquid waste only when below a certain limit of activity concentration, which have been defined to bring no harm to the population or environment (as far as statistics and current scientific knowledge tell us, of course). The same goes for dose rates allowed in the environment. For example, in Europe where I work, the limit of concentration for Cs-137 is 70 Bq/l for water release in sewers, and for solid waste, the maximum specific activity is 1000 Bq/kg. For dose rates in the environment, 0.5 µSv/h is the maximum allowed in normal conditions, but it can go up to 10 µSv/h for accidental conditions (or respectively 1 mSv/y and 20 mSv/y).

This kind of data can be used to compare correctly the values measured in the different studies that you describe, and the limits for all isotopes can easily be found for each country.

One thing which I did not see in the comments: the ultimate reference point for us working in the radioprotection field is the ICRP (http://www.icrp.org/), which is the common basis on which all countries rely for scientific knowledge and to establish regulations. Other official agencies, such as the UNSCEAR (UN’s own body for radioprotection) are notoriously more biaised as pro-nuclear, while the ICRP tries to remain as neutral as possible (which is not easy).

I have found out what kind of chemical reaction could happen to fuel rods with zirconium cladding while on a pool (either in the reactor or in a spent fuel pool): water steam at high temperature can oxidize Zr to generate Zirconium oxide and gaseous hydrogen.

Even though this is an unlikely reaction to happen under normal operational conditions, it could happen if there is an accident that allows the temperature of the rods to rise.

After some search, I found the following document with a study on this concern:

BTW, many of us may remember the flash cubes used with Kodak Instamatic cameras: that flash used Zirconium foil.

Zirconium powder is very flammable , depending on the size of the particles: the smaller the particle, the more flammable it is because the reaction rate is increased with an increase of the surface area of contact between Zr and the air, with fine Zr powder it could ignite even at room temperature.

Zirconium foil is not as flammable as the powder, for the foil needs a much higher temperature for the reaction to start (ignition temperature is dependent of the thickness of the foil, with lower temperature for thinner fils), above 600 °C.

Solid Zirconium does not present this level of reactiveness, but can react with water steam at high temperatures, as I have already mentioned above.

I also found the following news from a research team at MIT on the substitution of Zr cladding with “safer” Silicon Carbide cladding, and how this line of research was promoted by the Fukushima accident:

The aforementioned news article from MIT is interesting, among other things, because it mentions the following:

“Kazimi and his colleagues not only tested the material’s response under normal operating conditions, with temperatures of 300 degrees Celsius (572 degrees Fahrenheit), but also under the more extreme conditions of an accident, with temperatures up to 1500 C (2732 F).”

Thanks! Gradually assembling all this info into a picture… but it’s a hazy one. At least it is clearer to me now why the level of damage to the rods in the pool is a major source of uncertainty in the risk profile.

An excellent discussion. I am not qualified to comment on specifics, and frankly I am suspicious of the honesty and transparency of certain parties involved in Japan. However, I greatly admire your desire to uncover real hard data with regard to Fukushima.

My comments and questions relate to “CANDU” reactor design created in the 1960’s which makes use of ordinary (un-enriched) uranium and heavy water to generate power versus the typical Light Water Reactor (LWR). If I remember correctly the CANDU design was called “the poor man’s nuclear reactor” since it did not require the very expensive enrichment of uranium or a heavy pressurized containment vessel which certain countries lacked the technology to construct.

So if you are a nation starting down the nuclear road – and you have no intention of building nuclear weapons, for which the enrichment of uranium is required, this would be a reactor design to consider. CANDU reactors were constructed in the 60’s and 70’s and operate to this day in Canada, India and China.

Anyway beyond the fact that enrichment of uranium was not needed, what really stands out in my mind is that the CANDU design is inherently safer than the LWR design. In an emergency the heavy water could easily be gravitationally flushed as moderator and primary coolant and replaced with ordinary water which ONLY acts as coolant with ordinary (un-enriched) uranium. Additionally the spacing in between the uranium fuel clusters is greater than in a LWR. I seem to remember that this was considered one of the major drawbacks of this design – the core took up more horizontal real estate than then a comparable LWR. However, the spacing provided the opportunity to place shut-down rods above the core held in place electromagnetically – which in the case of complete loss of electrical power, would fall into the core under gravity making meltdown impossible.

Most people, including a few with physics backgrounds, have no idea that this design exists, and some have even insisted (until I tell them to check it out on the internet) that it is impossible to have power generation using ordinary uranium.

My questions are as follows:

If Iran insists that they are only interested in the ‘peaceful use’ of nuclear energy, why are they enriching uranium on a massive scale, when they could be building reactors of the CANDU design? Why have I never seen any response to their claim of peaceful use that even mentions the CANDU design?

I know that if you are a nuclear nation (or trusted ally of one) and have the facilities to enrich uranium it is cheaper (less real estate required, and no heavy water required) to build a LWR, but considering the potential failure modes of the LWR versus the CANDU is it penny-wise but pound-foolish for the nuclear nations to go the LWR route?

Matt – if you open up a more general discussion I would be interested in any comments in response to this as well as answers to these questions. Maybe I’m way off base factually, as I’m writing this from memory, but I would like someone to tell me so…

Hi professor, and fellow readers of this blog. I wanted to share an article I read recently on the situation at Fukushima. It sounds quite grave, but as I am not an expert in this field, I was hoping you might take a look and hopefully share any insight you might have.
“Fukushima – A Global Threat That Requires a Global
Response”

Well, the one thing I’m sure of is that the people who wrote this aren’t experts and don’t really understand what they’re saying. They are both overstating and misstating some of the risks, and not putting things in context. It’s very scary to say “three reactor cores have gone missing.” That’s certainly not true. Three reactor cores have melted down — that’s bad. But it’s not as though their location is completely unknown; water is keeping them cool, so the rough location of the fuel is most certainly known. It would be better if more were known; but to suggest that nothing is known is to scare people.

“An estimated 300 tons (71,895 gallons/272,152 liters) of contaminated water is flowing into the ocean every day.” That’s not very much. The Pacific Ocean is enormous, and the degree of contamination is not so extreme that this represents vast amounts of radioactivity. Scare-mongering, that’s what this is. “The first radioactive ocean plume released by the Fukushima nuclear power plant disaster will take three years to reach the shores of the United States. This means, according to a new study from the University of New South Wales, the United States will experience the first radioactive water coming to its shores sometime in early 2014.” So what? It all depends *how* radioactive that water is; if it’s very lightly radioactive it will have no affect on anybody. Everything around you is already a bit radioactive, so we have to find out — is this a tiny amount of radioactivity, or a lot? The writers never address this at all, taking it for granted that any amount of radioactivity is a terrible, awful thing — which isn’t true. Scare-mongering, again.

“independent research is showing that every bluefin tuna tested in the waters off California has been contaminated with radiation that originated in Fukushima.” Again — how much are we talking about? It’s very easy to detect radiation, even at levels far, far lower than the ambient radioactivity in the stonework in your house, or the levels that you’d be affected by in an airplane. The authors don’t seem to know this. Again, scare-mongering.

“When contact with radioactive cesium occurs, which is highly unlikely, a person can experience cell damage due to radiation of the cesium particles. Due to this, effects such as nausea, vomiting, diarrhea and bleeding may occur. When the exposure lasts a long time, people may even lose consciousness. Coma or even death may then follow. How serious the effects are depends upon the resistance of individual persons and the duration of exposure and the concentration a person is exposed to, experts say.” Terrifying!!! Do you realize how large the exposure would have to be, compared to how much is in the fish? There’s nothing in the fish that could possibly cause this level of problems for you, even if you ate this fish every day. Again, scare-mongering.

“Wasserman reports that some say this could result in a fission explosion like an atomic bomb,” Just plain false. False, and absolutely unacceptable for the people who are writing this to say so. These people should be fired.

I have to go deal with some other things; I can’t finish this right now. But suffice it to say — this is exactly the sort of thing that motivated me to start some web posts about this. We cannot accept people throwing scary ideas around like this, with no context, plenty of errors, and a mish-mash of facts and stories.

Thanks for taking the time to go through that article. I’ll be more wary about articles such as these. To their credit, the authors do support the call for a group of independent nuclear experts to take over responsibility for the reactor site from TEPCO, which I think is a good idea. I wasn’t sure where to go for the most accurate information..free from agendas, falsities, or misinformation. I’m glad you started this conversation. The posts on this topic are extremely helpful to me, and I’m sure for others as well, who are looking to inform themselves on just what is going on in Fukushima.

It is a neat in addition to very helpful item of facts. I will be delighted that you discussed this convenient details here. Be sure to continue to be us up to date such as this. Many thanks giving.

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